A bladder type tire vulcanizing machine has heretofore been known. In this type of a tire vulcanizing machine, a bladder is installed inside a green tire set within a mold. The bladder is an elastic diaphragm for the transfer of fluid pressure and is composed of a material (e.g., butyl rubber) having elasticity. It is capable of expansion and contraction. A heating/pressurizing medium such as steam or high-temperature gas (e.g., inert gas such as nitrogen, or air) is supplied to the interior of the bladder. As a result of this supply, the bladder expands and presses the green tire against the mold. Further, the heating/pressurizing medium and the mold heated by the heating/pressurizing medium heat the green tire from both inside and outside of the tire, thereby vulcanizing the green tire.
In connection with such a bladder type tire vulcanizing machine, the technique disclosed in Patent Literature 1 or 2 has heretofore been known.
In Patent Literature 1 there is disclosed a tire vulcanizing machine for heating the aforesaid heating/pressurizing medium at a high heat exchange rate. This conventional tire vulcanizing machine is provided with jet means for jetting a heating/pressurizing medium for vulcanizing/molding of a green tire to the interior of a bladder and is also provided with means for heating the heating/pressurizing medium at a high heat exchange rate by electromagnetic induction heating for the jetting means.
In Patent Literature 2 is disclosed a tire vulcanizing machine wherein means necessary for agitation and heating of the aforesaid heating/pressurizing medium are disposed concentratedly within a utilizable space inside a green tire. This conventional tire vulcanizing machine has a turbine and an electric motor for operating the turbine. And the turbine, a rotor and a stator of the electric motor are accommodated within a sealed space into which the heating/pressurizing medium is supplied.
However, all of the above conventional techniques involve the problem that a marked temperature difference occurs between upper and lower portions of the green tire in the vulcanizing process and it obstructs the stabilization of the tire quality.
More particularly, the tire vulcanizing machine according to each of the above conventional techniques has a supply section for supplying the heating/pressurizing medium from a lower side and upper and lower gripping sections for grippingly holding upper and lower edge portions of the bladder respectively.
On the other hand, in such vulcanizing/molding using the heating/pressurizing medium as described above, a set temperature of the heating/pressurizing medium supplied to the interior of the bladder is usually set higher than a set temperature of the same medium after a temperature rise and also higher than the mold temperature after the temperature rise. This is for increasing the rate of temperature rise in an initial stage of vulcanization. When such a high-temperature heating/pressurizing medium is conducted from the lower portion of the vulcanizing machine to the supply section through a pipe or the like, the heat of the pipe or the like is transmitted particularly to the lower gripping section by heat conduction and then transmitted from the gripping section to a lower edge portion of the green tire. If a metallic contacting section adapted to come into contact with the lower edge portion of the green tire to support the lower edge portion is present between the lower gripping section and the green tire as described in Patent Literature 1, the aforesaid heat conduction to the lower edge portion of the green tire becomes more marked. Such unbalanced heat conduction to the lower edge portion side of the green tire contributes to increasing the temperature difference between upper and lower portions of the green tire during vulcanizing/molding. This causes the problem that the vulcanization proceeds more rapidly at the lower edge portion of the green tire, i.e., on the high temperature side, than at the upper edge portion of the green tire, i.e., on the low temperature side, resulting in production of a tire not uniform in the quality of material (that is, the vulcanization quantity differs between upper and lower portions), thus exerting a bad influence on the tire quality.                [Patent Literature 1] Japanese Patent Laid-Open No. 2005-22399        [Patent Literature 2] Japanese Patent Laid-Open No. Hei 07 (1995)-329066        